Sensitive switch



` Jan; 26, 1943. B. w. wlLLl'AMs ETAL 2,309,230

SENSITIVE SWITCH Filed July 28, 1941 sheets-sheet 1 Jfyvf 3 *V mh@ i@ L@ 3;? 35 21g @fg 5f 22 27 2 I [/22 1,1/ Clo 2 T l -Ii WL :LW-' )l s. JF

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a w. WILLIAMS ETAL SENSITIVE SWITCH Filed July 28, 1941 2 Sheets-Sheet 2 NVENTOR5 Patented Jan. 26, 1943 OFFICE SENSITIVE SWITCH Eradlee W. Williams and Homer S. Williams,

Chicago, lll., assignors to Tech Equipment Company, Chicago, Ill.

Application July 28, 1941, Serial No. 404,304

14 Claims.

This invention has as its principal object the provision of improvements in electric switches, especially those adapted to be actuated by delicate and slightly moving actuating means.

More specifically it is an object to provide a sensitive switch adapted to be actuated by an operating member subject to irregular movements and displacements, but normally moving only slightly or imperceptably and with relatively little driving force.

Still more specifically, it is an object to provide a sensitive switch adapted to be actuated by a bellows or iiuid displacement device to respond to delicate pressure changes on the one hand, and to adjust itself automatically to abnormal operations of the bellows, responsive to large displacements, on the other.

A further object is to provide a switch having an impositive and adjustable driving connection with an operating means which is subject to movements in excess of the normal operating movements of the switch. y

Further objects are to provide a switch which includes one or a plurality of contact arms having an impostive driving connection with a driving member, and means including such connection providing leverage which will cause the arm or arms to move great amounts responsive to trifling movements of the driving member; to mount a plurality of such arms with different leverages and thereby provide a differential adjustability thereof which will cause the switch arms to maintain a practically constant operating relationship, regardless of the displacement of the driving member; to provide certain` auxiliary switch means serving also as a stop or limiting means for other switch parts.

Other objects, advantages and novel aspects of the invention reside in details of construction, as well as the disposition, mode of operation and integration of the component parts of the illustrative embodiment shown in the annexed drawings in which:

Fig. 1 is an elevational view of one form of the switch;

Fig. 2 is a horizontal section along lines 2 2 of Fig. 1;

Fig. 3 is a vertical section along lines 3--3 of Fig. 1;

Fig. 4 is an elevational view of a modified switch structure;

Fig. 5 is a view looking down on the device of Fig. 4;

Fig. 6 is an exploded perspective of essential elements of the modified structure of Figs. 4 or 5; 55k

The form of the invention shown in Figs. 1 to 3 is divided from our U. S. Letters Patent No. 2,249,370, filed March 20, 1940, and issued July 15, 1941, relating to a pulse count and blood pressure apparatus in which, among other things, pressure variations in an artery under test are sensed or detected by means including some kind of tourniquet or arm band having an inflatable cushion or bag member strapped thereby against the arm, for example, and adapted to be iniiated by fluid pressure until the pressure variations in the artery cause corresponding pressure variations in the cushion or bag and the pressure system ci which it is a part.

While the present novel switch structure is especially useful for actuation by slight operating movements or forces such as would be occasioned by arterial pulses, for example, it will be readily apparent to those skilled in the various arts, that the switch is adaptable to many other applications where the displacement of an operating member may be very slight at one time and very great at another; or where little force is available to aotuate the switch.

For these reasons, the following description is not to be construed as limiting the application of this useful device, but rather as merely exemplary.

Referring to Fig. 1, the switch is preferably mounted on a panel I0 of insulating material, to which there may be attached some form of hanger bracket I I for mounting purposes.

As viewed best in Fig. 3, a stationary contact I2 is screw-threaded into a metallic cleat I3, se-

. cured to the back of panel IU by means such as a screw I4. A lead wire I5 is soldered to the cleat for a circuit connection to this contact, the contact end portion I2a of which projects through a hole I6 in the panel.

On an opposite face of the panel is disposed another stationary contact I8 mounted on an insulating block I9 against the panel by screws 20, one of which connects with a lead wire 2I for another circuit connection.

Referring now particularly to Figs. 1 and 2, a movable contact in the form of a long arm 22 has one (right-hand) end 22a disposed somewhat loosely in a space 23 formed between two metal pieces 24 and 25 spaced apart by a third spacer piece 26 clamped between the other two pieces by action of mounting screws 2I passing through all three pieces to engage fastening nuts 28. This arrangement provides a loose pivot point for the long lever arm, the opposite or contact end 22b of which is disposed between contacts I2 and I8.

A lead wire 29 connects the movable contact in circuit. In the present arrangement, means for moving the movable contact comprises a reciprocable member or rod 30, attached to its inner end 3i (Fig. 2) to a metallic bellows 32, seated at 33 in a metal housing or shell 34, which is secured to the back of the panel by nuts with the rod 30 projecting through a hole 36 (Fig. 2) in the panel, and thence loosely through the contact strip 22 at 3l.

While the switch will obviously cooperate equally well with any operating member, such as rod 36, adapted to move back and forth greater or less amounts, the illustrative embodiment employs the bellows to eiect such movements, there being a nipple 4Q adapted for connection to the hose of an air pressure line, and another nipple KH, also adapted for connection in said line.

Variations in pressure in the aforesaid air line cause expanding and collapsing movements of bellows 32 with corresponding reciprocation of rod 30.

The contact strip 22, being loosely secured at its end 22a, bears its weight against rod 30 with suilicient force to cause a frictional drivingT engagement therewith such that the contact strip moves back and forth with the rod between the limits permitted by contacts l?. and I8.

Because the switch is especially suitable for sensitive setting and operation, the clearances between contact 22 and the stationary contacts are usually very slight, of the order of two or three one-thousandths of an inch; and because of the mechanical advantage possible by the length of the contact in comparison with the length of the lever system between rod 30 and the supported or fulcrumed end 22d of the contact strip, very slight movements of rod 39 cause relatively greater movements of the contact end 22h.

In addition to the feature ci sensitivity, is another of self-adjustmenL with respect to varying displacements of rod 3Q. By virtue of the impositive or weight-effected frictional driving connection between rod 30 and movable contact 22, the rod 3G may shift in and out relatively great amounts, notwithstanding that the movable contact is limited to displacements of a few thousandths oi an inch, rod 30 simply slipping through the hole at 3l in contact 22.

It frequently happens that a sudden pressure change of considerable magnitude will occur in the air line, causing rod 30 to be projected outwardly as much as ve-sixteenths or even an half an inch, whereupon the relatively slight pressure variations will continue to cause rod 30 to move back and forth, carrying contact 22 therewith for positive contacting engagement with contacts I2 and I8. The neness of .the response to pressure variations may b-e regulated by adjusting contact I2.

In Figs. 4 through 6 there is shown a modiiied form of this switch wherein one of the socalled stationary contacts is arranged for automatic adjustment under control of the actuating means, for example the rod 3Q.

This modied arrangement is especially suited for use with a cardiometric or blood pressure apparatus such as set forth in our copending application S. N. 402,358, nled July 14, 1941, wherein only one pressure bag or tourniquet is utilized to apply an occluding or artery-co1- lapsing pressure, and to detect pulsations when the blood flow is resumed. In this kind of an arrangement the pressure on the bellows 32a may often go as high as 160 mm. of mercury, or as low as mm. of mercury, with correspondingly strong or weak pressure variations in response to strong or weak arterial pulses. The present arrangement adjusts the contact system accordingly.

In Fig. 5, the modied switch is mounted on the same kind of a panel I0a as in the previously described arrangement, these being, in addition, posts IGZ: to receive a cover, not shown. As in the device of Fig. 2, the actuating means is illustrated as a bellows 32a housed in a shell 34a secured to the panel by screws 35a.

The bellows rod 30a in this case passes freely through the panel, as before, and freely or loosely through a hole 5I in a main movable contact strip 59 (Fig. 6) which rests by its weight upon the rod 33a as in the previously described arrangement.

At one (right-hand) end the contact strip E0 is oiset laterally as at 52, and the oiset fits loosely in a slot (not seen) in bracket 53, which constitutes a pivot or fulcrum point for this contact. The opposite or left-hand end 50a of the movable contact is preferably treated with a suitable non-corroding contact alloy sweated thereon.

Another elongated Contact strip EE] has a contact area 60a near its left end for cooperation with area Sd, and is secured, as by rivets 6I to a non-conductive plate 62 of Micarta or the like, having an over-size hole 63 therein through which rod 30a passes.

At its end 63D (Figs. 4 and 5) Contact 69 rests freely but snugly in a slot (not seen) formed in a bracket Si secured as at 65 to the panel, which constitutes a pivot point or iulcium for this second, self-adjusting contact.

It will now be apparent that the two long contacts 5G and 60 are movable with respect to each other by a common driving or actuating agency, namely rod 30a; and that the levers are reversely fulcrumed with respect to the common driving means in such manner that whereas one contact (59) moves a relatively great amount responsive to slight displacements of rod 30a, the other contact (60) moves only trilling amounts for the same displacement of rod 30a. In fact for a normal operating displacement of rod 30a, which would be sui'licient to cause a movement of two or three thousandths of an inch of the contact end 58a of Contact 53, contact portion 60a of the other contact 6G may be considered as a practical matter to move not at all.

An adjustable stationary contact 'I0 is threaded into a cleat lI secured by nut and bolt means "I2 so that the contact end la (Fig. 6) is disposed to be engaged by contact area o'a on the main movable contact in one direction of movement of contact 50; contact area Ea engaging Contact portion Sila in the opposite direction of movement of contact 50.

The movable contacts are prevented from shaking off rod 30a by a cotter pin I4 (Fig. 4) passed through rod 3a.

A combination supervisory switch and stop means 8U is mounted on the panel and includes a pair of springy contact blades 8I and 82 secured and biased in normally spaced or open-circuit relationship between insulating wafers 33 in a pile-up or stack of conventional form. The end Bla of one of these contact blades extends in the path of outward movement of the insulating plate 62 so as to be pushed by the latter, upon substantial outward expansion ofthe bellows, into engagement with contact 82 to close any desired supervisory or auxiliary circuit desired in connection with the operation of the apparatus with which the sensitive switch may be used.

Stop means is provided in .the form of a third springy leai or arm 85, also secured in the switchstack, and having an offset nose or end 86 which lies in the patch of plate 62 to stop the latter in its normal operative position upon initial outward or expansive movement of bellows rod Sd, such initial outward movement of the rod frequentiy being considerable in certain installations, as for example the blood pressure apparatus hereinbefore alluded to, wherein the bellows is connected in circuit with a fluid pressure line and an arm tourniquet for applying a pressure to an artery. If, in such an application or arrangement, the patrons arm should suddenly be moved in the tourniquet, there would be a relatively great thrust or retraction of bellows rod 30a of a magnitude far in excess of the minute distance which the movable contacts could be displaced if it were not for the impositive connection with the bellows rod.

In operation, the arrangement of Figs. l through 3 is such that regardless of what position the actuating or driving means or bellows rod Sil assumes upon initial or subsequent adjusting movements of the bellows, there will be no resistance from the movable Contact, and no damage thereto or interference with the otherwise sensitive setting and operation thereof responsive to the normal, expected, slight displacements of rod 3l) to which the switch means is ordinarily intended to respond.

In the dual contact arrangement of Figs. Il through 6, the operation of the main movable contact 5l) is the same as that of Contact 22 in the previously described device.

Assume, however, that the bellows rod Sila moves outwardly (downward as actually viewed in Fig. 5) then the self-adjusting movable contact (i0 will be carried outwardly a considerable distance at its end on plate 62, but a relatively lesser amount in the region of its contact Gila.

But if bellows rod 30a makes an initial outward movement of only three-sixteenths of an inch or some other small amount, the outward movement of contact portion ia relative to a fixed point such as stationary contact 'IS-JEM, would be proportionately slight.

In terms of the magnitude of the available operating displacement or force for the switch, the first example, where the bellows rod makes a large initial displacement, is comparable to the situation, in the aforesaid blood pressure apparatus, where the subject has a relatively high pressure and strong pulse, because it takes a relatively high applied pressure (say 150 mm. of mercury) to equal the arterial pressure. Under these conditions, it is desirable to have the gap between the contact parts Ella-60a, 'ma somewhat wider, especially if the pulses are strong, as they are likely to be at that pressure level.

On the other hand, in the second example, where the bellows rod moves outwardly only a small distance, the situation is comparable in a blood pressure apparatus to the case where the patrons blood pressure is lower, say about 110 mm. Hg, in which case the total pressure in the arm band or tourniquet would be correspondingly low, and the pulses would in all likelihood be correspondingly weaker, so that it is desirable to have the contact gap smaller, for a weak pulse naturally means a smaller displacement of the operating means or bellows rod, and a correspondingly smaller displacement of the movable contact.

The foregoing automatic adjustment of the contact system for relatively slight or considerable gapping or displacement, depending upon the position initially assumed by the reciprocable operating member is made possible by the described reversely fulcrurned and levered arrangement of the contact elements.

The preferred embodiment of the invention set forth herein has been described in detail for purposes of illustration, it being understood that the objects of the invention may be realived by other forms and arrangements of the specific means set forth, so that the invention is not to be limited to any precise details of form, location, or function except as may be provided hereinafter in the appended claims.

Having thus described ourl invention, what We claim as new and desire to protect by Letters Patent of United States is:

1. In a sensitive switch, a long contact loosely held at one end and movable horizontally back and forth to engage contact means near the opposite end, and a horizontally reciprocable operating device movable transversely of the length of the long contact and upon which and between the ends of which the latter contact rests by gravity for impositive driving connection therewith so as to be carried with the operating device in all movements thereof.

2. A switch comprising a reciprocable driving member, a long contact arm having an opening therethrough between its ends and through which said member projects with the arm resting by its weight thereon such that said arm tends to move back and forth with said driving member, Contact means situated near one of the ends of the arm for electrical cooperation therewith during at least one of the back and forth movements thereof, and means adjacent the opposite end of said arm for limiting the freedom of movement thereof so as to cause said firstmentioned end of the arm to be displaced relative to said contact means by lever action under urgence of said driving member.

3. In a switch, reversely fulcrumed cooperating contact members, and an operating member common to said contact members and having driving connection with one contact member at a point closer to the fulcrum thereof than to the fulcrum of another said contact member whereby to provide a differential actuating leverage for said contact members to actuate the same cooperatively in circuit-controlling operation.

4. In a switch including a reciprocable driving member, a pair of contact arms extending transversely of the movement of said member and each drivingly associated with said member at a point between the respective ends thereof, and means for limiting the movement of an end region of each contact arm to provide for differential movements thereof responsive to movements of the driving member.

5. In a switch, a reciprocable driving member, a pair of normally gapped cooperating contact arms and means operatively associating the same with said driving member in such manner as to be moved by said driving member different amounts for a given displacement of the latter, one contact arm being thereby moved into and out of contacting engagement with the other responsive to reciprocations of said driving member, and the gap distance between said arms being varied in accordance with positions of greater or less advancement or retraction of the driving member with respect to its path of reciprocation when said arms are reciprocated thereby.

6. A self-adjusting switch for use with an actuating element movable back and forth, said switch comprising a first Contact arm rocked back and forth by said element, a second contact arm positioned to be contacted by said first arm in one of the directions of movement thereof, said actuating element being adapted to advance various amounts from a normal position in the direction of reciprocation dependent upon different operating conditions, said second contact arm having operative connection with said actuating element so as to be moved by advancing movement of the latter, as aforesaid, to adjust the contact gap between said arms to a greater or lesser amount dependent upon whether the advancing movement aforesaid is great or small.

7. A switch for use with a reciprocable actuating element which may assume different positions of projection or retraction in the direction of reciprocation thereof at diferent tirnes, said switch comprising: a rst Contact arm fixed near one end and having driving connection with said actuating element to provide a mechanical advantage Which will cause the opposite end region of the arm to move in amplified displacement; a second contact arm having driving oozmection with said actuating element at a point adjacent one end of the said second arm, the latter having an opposite end region disposed for contacting cooperation with said rst arm, and means irniting the possible movement of said opposite end region of the second arm in a manner which will widen the contacting gap between said arms in a predetermined proportion to the degree of projection or retraction of the actuating element, while causing only negligible displacement of the second arm with respect to the rst arm for normally small reciprocating movements of the actuating element, whereby a predetermined operating relationship may be maintained between said arms for all conditions of projection and retraction of said element.

8. The construction defined in claim further characterized by the provision of means for limiting the movement of each said arm in one direction opposite from the limited direction of the other.

9. The arrangement deiined in claim 'l further characterized by the provision of a stationary contact member also disposed as a movement limiting means for said rst contact arm, and stop means for limiting the movement of the second arm, at least, in a direction away from said stationary contact means.

10. In a switch, a plurality of contact arms and means mounting the same for lever-action movement, together with actuating means for said arms operatively associated with the latter to provide leverages of different degree such that the arms may be made to move diiferent amounts with respect to each other responsive to certain movements of said actuating means.

1l. In a switch automatically adjustable contact means including elongated, cooperable contact arms movable into and out of gapped and closed-circuit relation; actuating means for said arms adapted to assume different operating positions with respect to a fixed reference position and movable at any of said positions to effect normal switch-movement of at least one of said arms; and means providing a leverage connection between each of said arms and said actuating means so constructed and arranged that the gap distance between said contact arms is varied in proportion to the degree of movement of said actuating means with respect to said reference position and such that one of said arms will remain in effect and substantially motionless with respect to the other during movements of the actuating means in effecting the normal switchmovement of one of the contact arms as aforesaid.

12. Switch means as defined in claim l1 and further characterized in that said leverage connections are impositive.

13. Switch means as defined in claim 11 and further characterized in that said leverage connections are impositive, and there is additionally provided means for limiting the movements of said contact arms to amounts less than the maximum possible movements of said actuating means.

14. In a sensitive switch, the combination of an operating member adapted to move mainly back and. forth in an approximately horizontal plane but capable of limited motion in all directions; a long Contact and means securing the same near one of its ends in relative fixation at one side of said operating member with portions remote from said end resting on the operating member between its ends in the main direction of movement thereof in such manner that said contact is supported in an approximately horizontal plane and limitedly follows the movements of said operating member in all directions; and additional contact means engaged by said firstmentioned contact means in motion imparted thereto by movements of the operating member.

BRADLEE NV. WILLIAMS. HOMER S. VJILLIAMS. 

